The present invention relates to an improvement of a composite system (hereinafter “complex apparatus”) that can observe a sample with a scanning electron microscope (SEM) on a real time basis while machining the sample with a focused ion beam apparatus (FIB). The present invention also relates to an image noise removing or preventing method in the FIB/SEM complex apparatus.
There has already been publicly known a so-called double lens-barrel FIB system that is provided with an electron lens-barrel separately to have an observation function by an SEM in order to observe a machining state of a sample in applying etching and CVD to the sample with an FIB apparatus. In addition to functions for performing the etching and the CVD, the FIB apparatus includes a function as an ion microscope for detecting a secondary charged particle such as an electron or an ion emitted from a sample surface by ion irradiation and imaging an amount of the detection in association with an irradiation position. In response to needs for an observation of a sectional structure at a desired point of a semiconductor wafer, an LSI device, or the like, a conventional FIB apparatus has been used in a form of drilling a sample from a position above a sample surface with etching by FIB irradiation and inclining a sample stage to observe a cross-section of the sample. However, in this case, work of machining and observing a state of the machining has to be carried out repeatedly. Since an irradiation angle of an FIB has to be changed for the machining and the observation, the sample stage has to be moved every time the machining and the observation are performed. Therefore, there has been proposed a system in which two lens-barrels are arranged at different angles with respect to a sample surface to perform machining with one lens-barrel and perform a microscope observation with the other lens-barrel such that the processing and the microscope observation are performed by different beam irradiations. As a basic structure of the system, as shown in FIG. 9, an FIB lens-barrel 1 and an SEM lens-barrel 2 are fixed to a sample stage in an evacuated chamber 3 at different angles, blanking electrodes for switching and controlling beam irradiation are provided in the respective lens-barrels, and a secondary electron detector 4 is set near the sample stage. For example, a section machining observation apparatus described in a patent reference 1 has an object of solving problems in that operation is troublesome because the apparatus has to be moved between a machining angle (usually, horizontal) and an observation angle (about 45 to 60 degrees) several times, a mechanical error involved in movement of a sample occurs, and it is likely that a very small foreign matter or an abnormal shape is overlooked because a section cannot be seen during machining. In order to solve the problems, the apparatus of the invention described in the patent reference 1 includes an ion beam irradiation system and an electron beam irradiation system that irradiate beams on a sample surface to scan the sample surface, a detector that captures a secondary electron emitted from the sample at the time of irradiation of the respective beams, an image display device 6 that displays a SEM image 13 and/or an FIB image 14 based on an output of the detector, and a beam switch. The ion beam irradiation system and the electron beam irradiation system are arranged at an angle of 90 degrees or an angle narrower than 90 degrees from each other in irradiation axes thereof and are mounted in an identical sample chamber such that an ion beam and an electro beam can be irradiated at an identical point on the sample to scan the sample. FIG. 7A shows a form in which an electron beam of an SEM is blanked by blanking electrode 11 and an FIB is irradiated on a sample 10 and FIG. 7B shows a form in which an FIB is blanked by blanking electrode 12 and an electron beam of an SEM is irradiated on a sample 10. In this way, the beam switch alternately switches the ion beam and the electron beam, and the image display device 6 displays outputs of the detector 4 as a sample 10 surface image and a section machining image according to a switching operation of the switch.
According to the double lens-barrel FIB system described above, since it is unnecessary to perform inclined movement of the sample stage at the time of machining and at the time of a microscope observation, the double lens-barrel FIB system is advantageous in terms of trouble of operation and a mechanical error involved in the movement of a sample in the past. However, when it is attempted to perform a cross-section observation with the SEM during machining by the FIB, a secondary electron involved in the FIB irradiation is mixed in an SEM detection signal and becomes noise. In this phenomenon, for example, when it is attempted to drill a rectangular hole with FIB etching to observe a cross-section, the FIB is used to scan a rectangular area of the sample in a raster shape to machine the rectangular area. A secondary electron emitted from a sample surface by the beam irradiation is detected by the secondary electron detector. A signal wave form of this secondary electron changes according to a beam irradiation position as indicated as an FIB signal in FIG. 8. In addition, a secondary electron detection signal involved in the electron beam irradiation, which an operator desires to detect as a microscope image, is indicated as an SEM signal in FIG. 8. However, when it is attempted to perform an SEM observation in parallel at the time of the FIB machining, the FIB signal and the SEM signal are superimposed to be a secondary electron detection signal. The secondary electron detection signal changes as indicated as a signal at the time of FIG/SEM simultaneous irradiation in FIG. 8, and an image is disturbed by noise.
[Patent reference 1] JP-A-2-123749 “Section machining observation apparatus”, published on May 11, 1990, page 2 and FIG. 3.
A problem that the invention is to solve resides in providing a system including an FIB lens-barrel and an SEM lens-barrel in which, when a process of executing FIB machining is observed by an SEM on a real time basis, an influence of a secondary electron excited by FIB irradiation does not appear as noise in an SEM detection signal.